1. Field of the Invention
The present invention relates to a surface processing device and a method of processing a surface. It particularly relates to a surface processing device and a method of processing a surface which contemplate improvement in processing a surface of an object to be processed.
2. Description of the Background Art
Conventionally in the process for manufacturing semiconductor devices, various types of surface processing are performed, typically including film forming and etching. The film forming process includes the CVD method and sputtering.
An example of a conventional plasma CVD system will now be described with reference to FIG. 5.
A conventional plasma CVD system 300 has an electrode 306 and a holder electrode 308 contained opposite to each other within an evacuated container 304 which is evacuated by an evacuating device 312. Holder electrode 308 is grounded. Mounted on holder electrode 308 is a substrate 302 to the surface of which film forming process is applied. Substrate 302 is heated, for example, by a heater 310 within holder electrode 308.
A raw material gas 320 is introduced into evacuated container 304 via gas introducing portion 314 communicating with electrode 306. As raw material gas 320, SiH.sub.4 (silane)+H.sub.2 O is used, and recently, TEOS (tetraethoxysilane)+H.sub.2 O or the like has come to be used in view of processing at lower temperature and for planarization of silicon oxide films.
In plasma CVD system 300, gas introducing portion 314 is supplied with TEOS from a gas source 322 and H.sub.2 O from a gas source 324. Furthermore, mass flow controllers 326 and 328 are provided at supplying passages of TEOS and H.sub.2 O, respectively, and a heater 330 for vaporizing TEOS is also provided at the TEOS supplying passage.
Radio frequency (RF) power is supplied to the space between electrode 306 and holder electrode 308 from an RF generator 318 via a matching box 316. A continuous sign wave is used for the RF power and its frequency is generally 13.56 MHz.
In such a plasma CVD system, when raw material gas 320 as described above is introduced into evacuated container 304 to obtain a degree of vacuum, for example, of several hundred mTorr within evacuated container 304 while RF power is supplied to electrode 306 from RF generator 318, RF electric discharge is generated between electrodes 306 and 308, causing plasma 332 therebetween.
At that time, electrons are trapped in a blocking capacitor, which is generally contained in matching box 316, so that electrode 306 is negatively charged. This causes positive ions in plasma 332 to accelerate toward and collide against electrode 306 and electrons are thereby generated to maintain plasma 332.
Thus, due to plasma 332, raw material gas 320 is activated and chemical reactions proceed whereby a silicon oxide (SiO.sub.2) film is formed on a surface of substrate 302.
The reaction between the TEOS and H.sub.2 O described above can be expressed by the following chemical formulas: EQU Si(OC.sub.2 H.sub.5).sub.4 +H.sub.2 O.fwdarw.Si(OC.sub.2 H.sub.5).sub.4-n (OH).sub.n +C.sub.2 H.sub.5 OH . . . (hydrolysis reaction) i) EQU Si(OC.sub.2 H.sub.5).sub.4-n (OH).sub.n .fwdarw.SiO.sub.m (OH).sub.j (OC.sub.2 H.sub.5).sub.k +H.sub.2 O . . . (dehydrating condensation reaction) ii) EQU SiO.sub.2 +H.sub.2 O+C.sub.2 H.sub.5 OH iii)
TEOS=Si(OC.sub.2 H.sub.5).sub.4 PA1 silanol=Si(OC.sub.2 H.sub.5).sub.4-n (OH).sub.n PA1 silicon polymer=SiO.sub.m (OH).sub.j (OC.sub.2 H.sub.5).sub.k PA1 TEOS=Si(OC.sub.2 H.sub.5).sub.4 PA1 silanol=Si(OC.sub.2 H.sub.5).sub.4-n (OH).sub.n PA1 silicon polymer=SiO.sub.m (OH).sub.j (OC.sub.2 H.sub.5).sub.k
In the system of reaction between TEOS and H.sub.2 O, silanol is first produced by the hydrolysis reaction expressed by chemical formula (i). Then, by the dehydrating condensation reaction expressed by chemical formula (ii), silicon polymer having an appropriate molecular weight is produced from the silanol as an intermediate. The silicon polymer adheres to a surface of an object to be processed and is fluidized to realize a planarized film formed on the substrate surface. Thereafter, as expressed by chemical formula (iii), the silicon polymer also dehydrates to produce SiO.sub.2 and thus SiO.sub.2 film is formed on the substrate surface.
However, in the reactions in the above plasma CVD system, since a chemical reaction is caused by electrons of several eV, the molecules of the raw material gases are decomposed into many kinds of molecules. This practically makes it difficult to selectively cause only the above desired reactions.
In forming a SiO.sub.2 film by reaction between TEOS and H.sub.2 O, it is important to produce silanol by reacting TEOS, the molecular structure of which is kept intact, with H.sub.2 O maintained at high temperature.
However, while the decomposition of the new material gases by plasma partially excites reaction (i), Si and SiO produced by decomposition of TEOS directly reacts with O produced by decomposition of H.sub.2 O, for example, causing a reaction dominantly producing SiO.sub.2, rather than silanol, as the intermediate. Thus, it is not practically ensured that the films formed are adequately planarized by silicon polymer.
Furthermore, in the above plasma CVD system, since silanol is less produced and SiO.sub.2 in gas phase dominantly adheres to the substrate surface, flatness of the films cannot be achieved without keeping the substrate at a low temperature of at most 120.degree. C. and restraining the dehydrating condensation rate of the silanol.
Thus, since a SiO.sub.2 film thus formed on a substrate maintained at low temperature has not experienced adequate reaction, it contains a large amount of OH group and has shortcomings such as large leakage current and low dielectric strength.
Furthermore, when heat treatment (300.degree. C.-400.degree. C.) is performed after the film formation to improve film quality, volumetric shrinkage is caused and thus tensile stress is caused, resulting in cracks or the like in the film.